The invention relates to extreme pressure lubricating oils, particularly alkali metal borate-containing lubricants.
Alkali metal borate-containing lubricants are well known in the art for their usefulness as extreme pressure lubricating oils. See, for example, U.S. Pat. Nos. 3,313,727, 3,565,802, 3,819,521, 3,846,313, 3,853,772, 3,907,691, 3,912,639, 3,912,643, 3,912,644, 3,997,454, and 4,089,790.
The borate-containing oils, described in these patents, have a serious deficiency in service. If water is introduced into the system containing the borate lubricant, the borate crystallizes out of the oil and forms hard granules. This crystallization decreases the extreme pressure function of the lubricant. Furthermore, it has been found that water contamination of the borate lubricant can lead to seal leakage. It is believed that the crystallization is caused by water contamination which leads to the formation of deposits on shafts at or near the seals. The turning motion of the shafts then slowly abrades the seals, thereby allowing loss of the lubricant. Various alkali metal borate lubricants have been described in the patent literature as having improved properties relative to water contamination, e.g., U.S. Pat. Nos. 3,997,454 and 4,089,790. Both of these patents teach the use of dithiophosphates or salts of dithiophosphoric acid.
U.S. Pat. No. 3,997,454 claims a hydrated potassium borate with a boron-to-potassium ratio of 2.5 to 3.5 as being superior to other alkali metal borates in resisting the adverse effects of water contamination. Particularly preferred is a lubricant composition containing a potassium borate and antiwear agents selected from (a) zinc dihydrocarbyl dithiophosphate having 4 to 20 carbons in each hydrocarbyl group and (b) a C.sub.1 to C.sub.20 ester, C.sub.1 to C.sub.20 amide or C.sub.1 to C.sub.20 amine salt of a dihydrocarbyl dithiophosphoric acid or (c) mixtures thereof.
U.S. Pat. No. 4,089,790 claims a synergistic lubricant mixture containing (1) a hydrated potassium borate and (2) an antiwear agent selected from (a) zinc dihydrocarbyl dithiophosphate, (b) C.sub.1 -C.sub.20 ester, C.sub.1 to C.sub.20 amide or C.sub.1 to C.sub.20 amine salt of a dihydrocarbyl dithiophosphoric acid, (c) zinc alkyl aryl sulfonate and (d) mixture thereof, and (3) oil soluble antioxidant organic sulfur compound. This composition is disclosed as having improved properties relative to water contamination.
It is one object of the present invention to provide an alkali metal borate-containing lubricant containing amine salts of phosphate and/or monothiophosphates having improved resistance to the adverse effects of water contamination as compared to the prior art compositions containing dithiophosphates.